Vertex position for linked object with armature
After ask the question, I had an idea:

import bpy

a = bpy.context.object
if a.type == 'ARMATURE':
    grpname = a.proxy_group.name

    grp = bpy.data.groups[grpname]
    for o in grp.objects:
        if o.type == 'MESH':
            print(o.name)
            for m in o.modifiers:
                print(m.name)

            # Apply modifiers
            me = o.to_mesh(scene=bpy.context.scene, apply_modifiers=True, settings='PREVIEW')
            myvertices = me.vertices
            for v in myvertices:
                print(v.co)

            if me is not None:
                bpy.data.meshes.remove(me)

        print("===================\n")
else:
    print("No armature selected")


You can use the same code that I used in local mode.